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They aren't still using your data (after all, the apps are no longer installed so how could they?).
What this is showing is the total amount of data used in this billing cycle by these apps between the start of the current billing cycle and the time that you uninstalled them. Since there is no longer an app to associate this data usage with it shows the total usage by all apps that have been uninstalled during this billing cycle. It will disappear completely with your next billing cycle, unless you uninstall more apps during that period.
Edit: Andy's reply is of course much more concise than mine, while containing all of the important information...
Thats the amount of data they used before you uninstalled them....
I think it loses that information when you remove the app. I've never found anything that will show me it anyway.